A. Field of the Invention
The present invention relates to a method of training a grapevine for optimal fruit yield.
B. Description of the Prior Art
As members of the Vitis plant family, grapevines are climbing plants that are not self-supporting, unlike most trees. While grapevines have woody trunks, the weight of a vine's leafy canopy and grape clusters will often bring the vine's canes down towards the ground unless it receives some form of support. In viticulture, growers want to prevent any part of the canes from touching the ground because of the vine's natural inclination to send out suckers or basal shoots and take root in that area where the cane is touching the ground.
Other reasons for vine training involve setting up the vineyard and each individual vine canopy for more efficient labor usage or mechanization. Vines that are trained to have their “fruiting zone” of grape clusters at waist to chest height are easier for vineyard workers to harvest without straining their bodies with excessive bending or reaching. Similarly, keeping the fruiting zone in a consistent spot on each vine makes it easier to set up machinery for pruning, spraying and harvesting.
Most commercial grapevines are trained on a trellis system to manage the growth of the grapevine and to facilitate application of water, fertilizers, and insecticides. The trellis system also enables training the grapevine in a way to admit more sunlight to the interior canes for optimal fruit bearing.
Optimal vine training systems are designed to avoid excessive shading of the fruit by the leafy growth, the canopy. While some shading is beneficial, especially in very hot and sunny climates, to prevent heat stress, excessive amounts of shading can have negative impact on grape development. As a photosynthetic plant, grapevines need access to sunlight in order to complete their physiological processes. Even if the leaves at the top of the canopy are receiving plenty of sunlight, the young buds, grape clusters and leaves below will still experience some negative impact. During the annual growth cycle of the grapevine, excessive shading can reduce the success rate of bud formation, budbreak, fruit set, as well as the size and quantity of grape berries on a cluster.
The grape clusters themselves receive some benefit from getting direct sunlight through enhance ripening of various phenolic compounds that can contribute to a wine's aroma and quality. In addition to having decreased physiological ripeness, excessive shade will negatively impact a grape's quality by causing increases in the levels of potassium, malic acid and pH in the grapes while decreasing the amount of sugar, and tartaric acid. Beyond a lack of sunlight, excessive shading limits the amount of air circulation that can take place within a vine's fruiting canopy. In wet, humid climates poor air circulation can promote the development of various grape diseases such as powdery mildew and gray rot.
U.S. Pat. No. 3,585,756 describes training young fruit bearing canes to a wire so that the canes grow horizontally along the wire. This patent describes the grapevine canes trained to curve upward so there is only one canopy layer, not multiple distinct canopy layers.
U.S. Pat. No. 5,711,109 describes training a grapevine so that the fruiting canes grow in a horizontal canopy. However, the fruiting canes are not separated into different levels.
U.S. Pat. No. 6,578,318 describes a method of raising vine plants by separating the fruiting cane portion from the renewal cane portion. The fruiting canes are placed in an upper zone, and the renewal canes are placed in a lower zone. The fruiting canes are not separated into different levels.